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| author | Hans Verkuil <hverkuil-cisco@xs4all.nl> | 2023-09-07 10:54:31 +0200 |
|---|---|---|
| committer | Hans Verkuil <hverkuil-cisco@xs4all.nl> | 2023-10-07 10:55:44 +0200 |
| commit | cab0c4e94c49641563fa929af0cd6ffb62154acd (patch) | |
| tree | fd11c3a4a7c9fa6ffaf531c58e3659c465cb9698 /Documentation/userspace-api | |
| parent | 6496617b2b06d7004a5cbd53d48f19567d6b018c (diff) | |
media: Documentation: dv-timings.rst: explain basic approach
Explain how the DV Timings API and the V4L2_EVENT_SOURCE_CHANGE
event work together to handle video source changes.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Diffstat (limited to 'Documentation/userspace-api')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/dv-timings.rst | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/dv-timings.rst b/Documentation/userspace-api/media/v4l/dv-timings.rst index e17f056b129f..4b19bcb4bd80 100644 --- a/Documentation/userspace-api/media/v4l/dv-timings.rst +++ b/Documentation/userspace-api/media/v4l/dv-timings.rst @@ -33,6 +33,27 @@ current DV timings they use the the DV timings as seen by the video receiver applications use the :ref:`VIDIOC_QUERY_DV_TIMINGS` ioctl. +When the hardware detects a video source change (e.g. the video +signal appears or disappears, or the video resolution changes), then +it will issue a `V4L2_EVENT_SOURCE_CHANGE` event. Use the +:ref:`ioctl VIDIOC_SUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` and the +:ref:`VIDIOC_DQEVENT` to check if this event was reported. + +If the video signal changed, then the application has to stop +streaming, free all buffers, and call the :ref:`VIDIOC_QUERY_DV_TIMINGS` +to obtain the new video timings, and if they are valid, it can set +those by calling the :ref:`ioctl VIDIOC_S_DV_TIMINGS <VIDIOC_G_DV_TIMINGS>`. +This will also update the format, so use the :ref:`ioctl VIDIOC_G_FMT <VIDIOC_G_FMT>` +to obtain the new format. Now the application can allocate new buffers +and start streaming again. + +The :ref:`VIDIOC_QUERY_DV_TIMINGS` will just report what the +hardware detects, it will never change the configuration. If the +currently set timings and the actually detected timings differ, then +typically this will mean that you will not be able to capture any +video. The correct approach is to rely on the `V4L2_EVENT_SOURCE_CHANGE` +event so you know when something changed. + Applications can make use of the :ref:`input-capabilities` and :ref:`output-capabilities` flags to determine whether the digital video ioctls can be used with the given input or output. |